Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

Abstract

Dredge pumps are usually operated at part-load conditions, in which the low-solidity centrifugal impeller could experience large internal energy dissipation, related to flow separation and vortices. In this study, SST k-ω and SAS-SST turbulence models were used, in steady and unsteady simulations, for a low-head centrifugal pump with a three-bladed impeller. The main focus of the present work was to investigate the internal energy dissipation in rotating an impeller at part-load operating conditions, related to flow separation and stall. The unsteady nature of these operating conditions was investigated. Performance experiments and transient wall pressure measurements were conducted for validation. A methodology for internal energy dissipation analysis has been proposed; and the unsteady pressure fluctuations were analyzed in the rotating impeller. The internal power losses in the volute and the impeller were mostly found in the centrifugal pump. The rotating stall phenomenon occurred with flow separation and detachment at the part-load operating condition, leading to a dissipation of the internal energy in the impeller. The rotating impeller experienced pressure fluctuations with low frequencies, at part-load operating conditions, while in the design operating condition only experienced rotating frequency.The energy loss in the centrifugal pump could be divided into flow dissipation, disk friction, and discharge leakage loss. Kara Omar et al. [7] calculated the losses through empirical and semi-empirical models, and verified them with experimental results. El-Naggar [8] conducted an experimental one-dimensional flow analysis and predicted the pump performance in a dimensionless form. Klas et al. [9] performed simulations on a centrifugal pump and investigated the energy loss in different flow components, to detect the influence of the component geometry. These studies focused on the whole energy transformation in flow components, without a detailed loss analysis.The inner flow characteristic was investigated as the energy loss reasons for centrifugal pumps. Posa et al. [10] investigated the streamline distribution on the impeller blade surface and found that a stall phenomenon developed near the impeller shroud. Zhang et al. [11] applied velocity vector distribution to detect the flow pattern near the volute tongue, and to discuss its effects on the efficiency fluctuation of a centrifugal pump. Barrio et al. [12] detected a counter-rotating vortex near the interface between the impeller and the volute, through velocity distribution. Pacot et al. [13] used the pressure distribution to explore the stall propagation mechanism. Asim et al. [14] applied the Q-criterion to illustrate that a secondary flow generated near the volute tongue, with an impact on the pump head. Miorini et al. [15] and Zhou et al.[16] adopted a vorticity study to investigate tip leakage flow and rotating stall, respectively, to describe the development of these unsteady flow phenomena and to prove their effects on pump performance. These m...

Ways to reduce hydraulic losses in multistage centrifugal pumping equipment for mining and oil-producing industries

“…Based on the above graphical dependencies and previously obtained recommendations [10] on the choice of geometric and kinematic parameters of coaxially installed impellers, it was found that the coaxial arrangement of impellers in centrifugal pumps can reduce hydraulic losses by 23 %, and also contribute to an increase in pressure-fl ow characteristics, with unchanged overall dimensions of the unit.…”

“…When centrifugal pumps are not fully loaded, the pump impeller may experience internal energy dissipation due to fl ow separation and fl uid vortices. In order to establish the characteristics of the processes of dissipation of the internal energy of a centrifugal pump with a partial load, the authors of the article [10] investigated the unsteady nature of such operating modes.…”

Choosing the flow part geometric shape of the dredge pumps for viscous fluids

“…This direction includes studies devoted to the numerical simulation of unsteady flows in dredge pumps [2], [3]. They give a formalized approach to determining the internal energy dissipation during the rotation of a dredge pump impeller under conditions of its operation with a partial load caused by separation and stalls of the flow.…”

Dynamic Instability Analysis of a Double-Blade Centrifugal Pump

“…Recently, the flow instability of a multistage centrifugal pump a off-design conditions was investigated by Shibata et al [13]. Pressure pulsations at dif fuser inlet were measured and rotating stall phenomenon was observed with CFD tools In addition, some studies were carried out to do the deep analysis on the unsteady flow phenomena in centrifugal pump, for instance, flow separation [14][15][16], rotating stall [17 19] and recirculation [20,21]. Those directly cause the formation of flow instability pressure pulsations and pump vibration.…”